This invention relates generally to steam turbines, and more particularly, to controlling steam leakage paths in the turbine.
A steam turbine has a defined steam path which includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. Steam leakage, either out of the steam path, or into the steam path, from an area of higher pressure to an area of lower pressure may adversely affect an operating efficiency of the turbine. For example, steam-path leakage in the turbine between a rotating rotor shaft of the turbine and a circumferentially surrounding turbine casing, may lower the efficiency of the turbine and cause increased fuel costs. Additionally, steam-path leakage between a shell and the portion of the casing extending between adjacent turbines may reduce the operating efficiency of the steam turbine and over time, may lead to increased fuel costs.
To facilitate minimizing steam-path leakage between a High Pressure (HP) turbine section and a longitudinally-outward bearing, and/or between an Intermediate Pressure (IP) turbine section and a longitudinally-outward bearing, at least some known steam turbines use a packing casing that includes a plurality of labyrinth seals. At least some known labyrinth seals include longitudinally spaced-apart rows of labyrinth seal teeth which are used to seal against pressure differentials that may be present in the steam turbine. Brush seals may also be used to minimize leakage through a gap defined between two components. Although brush seals provide a more efficient seal than labyrinth seals, at least some known steam turbines, which rely on a brush seal assembly between turbine sections and/or between a turbine section and a bearing, also use at least one labyrinth seal as a redundant backup seal for the brush seal assembly. As a result, manufacturing and maintenance costs may be increased.
Other areas of steam path leakage within a turbine may also adversely affect turbine efficiency. For example, relatively large pressure drops across both the packing casing and a nozzle diaphragm may result in a plastic distortion and may result in a reduced steam turbine clearance.
In one aspect, a method of assembling a steam turbine is provided. The method includes positioning a sealing member in a leakage path defined between a first stage nozzle diaphragm and a packing casing, wherein the first stage nozzle diaphragm has a first coefficient of thermal expansion, and the packing casing has a second coefficient of thermal expansion, and coupling the first stage nozzle diaphragm and the packing casing such that the first sealing member is fixedly secured between the first stage nozzle diaphragm and the packing casing.
In another aspect, a seal assembly for sealing a leakage path is provided. The seal assembly includes a sealing member, and at least one coupling device extending through the sealing member such that the sealing member is fixedly secured between a first stage steam turbine nozzle diaphragm and a steam turbine packing casing.
In a further aspect, a rotary machine is provided. The rotary machine includes a first stage steam turbine nozzle, a steam turbine packing casing, a seal, and a plurality of bolts extending through the sealing member such that the sealing member is fixedly secured between the first stage steam turbine nozzle diaphragm and the steam turbine packing casing.